This invention relates to dynamoelectric machines, and in particular, to single phase induction motors. While the invention is described with particular reference to motors utilized in hermetic compressor applications, those skilled in the art will recognize the wider applicability of the inventive principles disclosed hereinafter.
There long has been a need for economical and efficient equipment in residential air conditioning applications. For example, in the past, it has been difficult to determine the proper size of available air conditioning equipment so that the installed equipment has ample capacity for peak load conditions, yet operates efficiently and provides suitable room temperature at light load conditions. Prior art attempts to solve the sizing problem generally make use of mechanical unloading devices in conjunction with the air conditioning or refrigeration system, for example, in order to provide proper regulation of the system. The terms refrigeration and air conditioning are used in their broadest generic sense, and are intended to include any system having a hermetic compressor as an element.
More recently, attempts have been made to modulate the compressor of the refrigeration system by operating the compressor at two distinct speeds. One solution to the motor design problem involving a modulated compressor application is disclosed in the co-pending application to Robert A. Landgraf, Ser. No. 723,989, filed Sept. 16, 1976, assigned to the assignor of the present invention, which is intended to be incorporated by reference herein.
Multi-speed motors are known in the art. In the past, multi-speed motors generally have been constructed by placing a plurality of distinct windings within a stator core, and thereafter switching between sets of distinct windings to vary motor speed. That is to say, for the purposes of this specification, "distinct windings" is defined to mean that each main winding physical pole of the dynamoelectric machine has a corresponding auxiliary winding physical pole that is energized only in conjunction with its main winding physical pole. In such multiple speed motors, the number of main winding poles equals the number of auxiliary winding poles, the poles of the main and auxiliary windings being physically displaced with respect to one another in order to generate the revolving field of the induction device.
While such multi-speed motor constructions work well for their intended purposes, they normally have been utilized in applications where slot fill of the motor is not critical. Slot fill is a term of art, and generally is expressed as a precentage of the total usuable slot area displaced by the motor windings for each slot of the particular lamination design used in constructing the core of the stator assembly. In many induction motor applications, slot fills are not critical, and ample slot space is provided in the lamination design for carrying a number of motor windings.
Hermetic motors, on the other hand, usually have high slot fill concentrations. One of the reasons for the high slot fill concentration is that motor performance and efficiency can be improved by utilizing additional material in the motor design, particularly by reducing the flux density of the core, either by increasing stack height or increasing the number of motor turns. Performance and efficiency can be varied in a number of other ways. As indicated, the number of turns used in a particular winding may be increased, or the winding resistance may be reduced by increasing the wire size used in the motor design. Both of these steps increase the physical space requirement of the winding. One or more of these design techniques commonly is used in hermetic motor developments in order to meet performance standards. Consequently, hermetic motors in general exhibit the highest slot fill percentages of all motor applications. For that reason, use of distinct multiple motor windings for attaining a multiple speed motor is not a practical design expedient.
An additional factor affecting the design of hermetic motors is the fact that the hermetic motor in use is enclosed and hermetically sealed in the compressor unit of the refrigeration system. Electrical connections for energizing the motor are made through the shell or enclosure of the compressor. The shell has a connection opening made in it, and a special connector that preserves the integrity of the refrigerant system is inserted in and hermetically seals the opening. The use and insertion of the connectors in the shells adds significantly to the compressor cost. Consequently, a general design requirement is that motors utilized in hermetic compressors be capable of electrical energization through a minimum number of leads in order to minimize problems encountered in making multiple openings through the compressor shell and resealing those openings with suitable connectors.
The motor design disclosed hereinafter meets these stringent design criteria by providing a multiple speed motor having a minimum number of motor leads, the motor exhibiting comparable performance at rated loads on either speed. In the preferred embodiment, the stator assembly of the motor has a single main winding constructed from a plurality of coil sets inserted in the slots of the stator core. The coil sets of the main winding define two physical motor poles. A first auxiliary winding and a second auxiliary winding also are provided, each being constructed from a plurality of coil sets. The coil sets of the first auxiliary winding also define two physical poles, while the coil sets of the second auxiliary winding define four physical poles. When two pole motor operation is desired, the main winding and two pole auxiliary winding are energized and the motor operates in a conventional manner as a two pole induction motor. When four pole operation is desired, the main winding is reconnected so that the polarities of the two physical motor poles produce four electrical motor poles, and the second auxiliary winding is energized. Thereafter, the motor operates as a four pole motor.
Those skilled in the art will recognize that interconnection and energization of the various windings may be accomplished automatically by suitable switching means. The arrangement disclosed utilizes a minimum number of windings, and requires only five external leads for passage through the compressor shell. The use of five leads on the motor results in a switch design more simplified and less costly over what would be required to change motor operating speed if the number of leads exceeded five.
One of the objects of this invention is to provide a multi-speed induction motor having a single main winding, and a pair of auxiliary windings, the single main winding being connected with respect ones of the auxiliary windings to provide two speed operation of the motor.
Another object of this invention is to provide a two speed hermetic motor for utilization in refrigeration compressors.
Yet another object of this invention is to provide a multi-speed motor having a minimum number of windings leads.
Another object of this invention is to provide a multi-speed motor in which a single main winding is utilized with multiple auxiliary windings.
Still another object of this invention is to provide an induction motor providing more efficient operation of a refrigeration system.
Other objects of this invention will be apparent to those skilled in the art in light of the following description and accompanying drawings.